Heat Exchanger
A heat exchanger is a device designed to transfer thermal energy between two or more fluids at different temperatures, without the fluids mixing. Heat exchangers are ubiquitous in engineering applications including power generation, chemical processing, HVAC systems, and automotive radiators. The rate of heat transfer depends on the temperature difference, the overall heat transfer coefficient, and the heat transfer area.
Key Formula
Q = U × A × ΔT_lm
LaTeX: Q = U \cdot A \cdot \Delta T_{lm}
| Symbol | Meaning | Unit |
|---|---|---|
| Q | Rate of heat transfer | W |
| U | Overall heat transfer coefficient | W/(m²·K) |
| A | Heat transfer surface area | m² |
| \Delta T_{lm} | Log mean temperature difference (LMTD) | K |
Worked Example
Problem
A shell-and-tube heat exchanger has an overall heat transfer coefficient U = 500 W/(m²·K) and a heat transfer area of 10 m². The log mean temperature difference is 40 K. Calculate the heat transfer rate.
Solution
Step 1: Identify given values — U = 500 W/(m²·K), A = 10 m², ΔT_lm = 40 K. Step 2: Apply the heat exchanger equation: Q = U × A × ΔT_lm. Step 3: Q = 500 × 10 × 40 = 200,000 W.
Answer
Q = 200,000 W = 200 kW
Common Heat Exchanger Types and Configurations
| Type | Flow Arrangement | Typical U (W/m²·K) | Common Use |
|---|---|---|---|
| Shell-and-tube | Counter-flow | 200–1000 | Oil refineries, power plants |
| Plate | Counter-flow | 1000–5000 | Food processing, HVAC |
| Double-pipe | Parallel or counter | 100–800 | Small industrial processes |
| Finned-tube | Cross-flow | 25–200 | Air conditioning, radiators |
| Spiral | Counter-flow | 500–1500 | Viscous fluid processing |
Interactive Tools
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Related Terms
Compressor (engineering)
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume, thereby increasing its energy content. Compressors are fundamental components in refrigeration systems, gas turbines, pneumatic tools, and industrial processes where pressurised gas is required. The work input to a compressor is governed by thermodynamic principles, and the efficiency of the compression process determines overall system performance.
Thermodynamic Cycle (engineering)
A thermodynamic cycle is a series of thermodynamic processes that return a system to its initial state, enabling continuous conversion of heat into work or vice versa. Engineering thermodynamic cycles such as the Rankine, Brayton, and Otto cycles form the basis of power plants, jet engines, and internal combustion engines respectively. The thermal efficiency of a cycle quantifies the fraction of heat input that is converted into net work output.
Diffuser (engineering)
An engineering diffuser is a component that decelerates a flowing fluid, converting kinetic energy back into pressure energy, thereby increasing the static pressure. Diffusers are used in compressors, wind tunnels, aircraft intakes, and HVAC systems to recover pressure with minimal losses. The performance of a diffuser is characterised by the pressure recovery coefficient, which compares actual pressure rise to the ideal isentropic value.
From the combination of "heat" (Old English "haetu", warmth) and "exchange" (Old French "eschangier", to swap). The engineering term came into use with the industrialisation of thermal processes in the late 19th and early 20th centuries.